Can global constants be declared in JavaScript?

Question

If so, what is the syntax for such a declaration?

Answer 1

If you only care about supporting newer browsers (or are using a transpiler such as Babel to support older browsers) you can do the following:

1. Create a settings.js file with whatever constants you want and export them:

export const FRUIT = "kiwi";
export const VEGETABLE = "carrot";

2. In files that you want to use them you could then import them as follows:

import * as Settings from './settings.js'

3. Then to use the constants do something like this:

console.log("The unchangeable fruit is " + Settings.FRUIT);

This is a much cleaner approach than trying to implement a global constant, especially when you have multiple JavaScript files that you want to use the constants in.

Answer 2

Everything is global unless declared with the var keyword.

There are no constants either. You can simply declare them without the var keyword.

If you want to ensure global scope you can throw it into the window object:

window.GLOBAL_CONSTANT = "value";

You can do this from within any scope. Constants can then be declared inside functions or closures, though I wouldn't recommend that.